For grieving widow Crystal Probst, the nightmare began two months ago with an alert sent from her husband’s Apple Watch.

Andy Probst, 64, was out for his morning bike ride on Aug. 14, when the device on his wrist detected a hard fall just blocks from his Las Vegas home. The device called 911 and alerted Crystal, his emergency contact, via text message.

Taylor Probst, Andy’s daughter, told ABC News, “Chopper was out. You could hear sirens in all different directions. And I vividly remember [my mom] turning to me saying, ‘That's for dad. That's for dad.'"

But Crystal and Taylor say they never could have imagined what happened to the beloved father and husband.

Probst, a retired police chief for Bell, California, was riding in the designated bike lane when a vehicle slammed into him, according to authorities. Two teenagers face murder charges in the alleged intentional hit-and-run.

“I saw everything, from where the phone was, where half of his helmet was and then where the bike was,” Taylor said.

Initially declared an accident, weeks went by before the shocking video of the alleged hit-and-run surfaced.

Authorities allege it shows then-17-year-old Jesus Ayala behind the wheel and 16-year-old Jzamir Keys recording the video from the passenger seat as they’re seen side-swiping a car. Police say the teens start laughing while one of them says, “Yeah, yeah, yeah, hit his a--” as the car pulls up behind Probst just before the fatal collision.

Authorities say the video was brought to the attention of law enforcement by a high school student who saw it and alerted their school resource officer.

“I can't think of too many cases I've ever had that -- where you have the audio, the video of what they're thinking and doing before the murder, as they commit the murder and after the murder. And there's just not many cases where you get all three of those,” Lt. Jason Johansson of the Las Vegas Metropolitan Police Department told ABC News.

Taylor says the now-viral video has haunted her since she saw it.

“We're happy that video exists because that's how it got switched over from an accident to a homicide. But we didn't want the entire world seeing it,” Taylor said.

Ayala, now 18, and Keys are accused of committing a series of crimes the morning of Aug. 14 -- three car thefts and three hit-and-runs, including the one that killed Probst, authorities said.

Both have been charged as adults with murder with use of a deadly weapon, battery with use of a deadly weapon and attempted murder with use of a deadly weapon. Ayala, who is accused of driving a stolen Hyundai Electra during Probst's alleged hit-and-run, is also charged with leaving the scene of a crash and possession of a stolen vehicle, among other charges.

Ayala and Keys pleaded not guilty to the charges.

Johansson alleges Ayala made statements to law enforcement on body camera footage after the alleged hit-and-run, saying he believed he was going to “get a slap on the wrist” and “be out in 30 days.”

“I think we all know now that probably is not going to be the case," Johansson said.

When asked about their reaction to Ayala’s comments, Taylor and Crystal did not mince words about the alleged killer.

“He’s an entitled little f---,” Crystal said.

“My reaction was, he doesn't, he doesn't even know what's f------ coming. Yeah, he is about to get slapped in the face real hard with reality,” Taylor said.

Meanwhile, the grieving daughter is now facing a future without her father.

“I'll never get to have my dad there, have that, you know, daddy daughter dance, have him give me away or anything like that, and that hurts. That hurts that was robbed from me. And that was robbed from my mom and my brother,” Taylor said through tears.

Crystal still sometimes wears her husband’s shattered watch that first alerted her to the unimaginable tragedy.

"Everybody says, you got to go get it fixed, but I don't know if I want to," Crystal said.

“It’s hard to grieve when you are so angry," she added.